FIG. 1 depicts a conventional perpendicular magnetic recording (PMR) head 10 used in recording a PMR media (not shown). The conventional PMR head 10 is typically used as a write head in a merged head including the PMR head and a read head. The conventional PMR head 10 includes a first pole (P1) 12, P1 pad 14, a first coil 16, insulator 18, a second pole (P2) 20, a magnetic pole layer (main pole) 22, write gap 24, a shield pad 26, a second coil 28, and shield 30. Although depicted as a single shield 30, it is typically composed of two portions 30A and 30B that are formed separately. The PMR head 10 is also depicted with two coils 16 and 28. However, PMR heads having a single coil may also be used.
In order to write data to a PMR media, the coils 16 and 28 are energized. Consequently, the main pole 22 is magnetized and the media written by flux from the pole tip 22A. Based on the direction of current through the coils 16 and 28, the direction of magnetic flux through the main pole 22 changes. Thus, bits having opposing magnetization can be written and the desired data stored on the PMR media. When the conventional PMR head 10 is not writing, no current is driven through the coils 16 and 28. When in this quiescent state, the remanence (zero current) magnetization of the poles 12, 20, and 22 is desired to be approximately zero.
The conventional PMR head 10 is desired to be used at higher recording densities.
In such applications, domain lockup, also termed remanent erasure, is an issue. Domain lockup occurs when the conventional PMR head 10 inadvertently erases data in the PMR media when no current energizes the PMR head 10. This occurs due to a remanent field remaining the main pole 22. Domain lockup is sensitive to the shape anisotropy of the pole tip 22A. A long nose length, NL, or the length of the pole tip 22A from the air-bearing surface (ABS) to the flaring point, is more likely to cause domain lockup. Without lamination of the main pole 22, the nose length typically must be no greater than about twice of the physical track width (perpendicular to the page in FIG. 1). Consequently, most PMR heads 10 have a short nose length. For such PMR heads 10, the primary cause of pole erasure is the magnetic domains in the yoke that may not fully relax after writing. Stated differently, the main pole 22 may not completely demagnetize after writing. Further, the pole tip 22A is sufficiently small that such deviations of the magnetization domains in the pole 22 from a perfectly demagnetized state may produce significant magnetization in the pole tip 22A. As a result, a high remanent field may be present in the PMR media even when no current is driven through the coils 16 and 28. This remanent field may erase data recorded on the PMR media after the head 10 passes over the media for many revolutions. Because it involves this inadvertent erasure, domain lockup is undesirable.
Domain lockup may result not only in inadvertent erasure of data, but also failure of the PMR media. The servo areas (not shown) of the PMR media are usually written at much lower linear density than the areas that store user data. Consequently, the servo areas are more subject to being erased by the remanent field of the PMR head 10. Erasure of servo areas may cause complete drive failure. Therefore, it would be highly desirable for domain lockup to be eliminated.
Various methods have been used to reduce domain lockup. These methods may have significant drawbacks. For example, FIG. 2 depicts a conventional PMR head 10′ in which domain lockup is attempted to be addressed. The PMR head 10′ contains components that are analogous to the conventional PMR head 10. Consequently, the PMR head 10′ is labeled similarly. The PMR head 10′ includes P1 12′, P1 pad 14′, first coil 16′, insulator 18′, a magnetic pole layer (main pole) 22′, write gap 24′, shield pad 26′, second coil 28′, and shield 30′. Note that the PMR head 10′ does not include a second pole analogous to P2 20. In addition, the conventional PMR head 10′ includes a small nonmagnetic layer 34 directly behind the main pole 22′. Although the PMR head 10′ has somewhat reduced domain lockup, it suffers from other drawbacks. In addition, the amount by which domain lockup is reduced may be relatively small.
Accordingly, what is needed is a system and method for reducing domain lockup in a PMR head.